ABSTRACT Campylobacter jejuni is a primary bacterial cause of gastroenteritis in the US and throughout the world, with 140 million cases worldwide and 1.3 million cases of C. jejuni gastroenteritis in the US each year. This infection leads to >30,000 deaths annually, primarily in children <5 years old in underdeveloped countries. Most cases of C. jejuni disease are sporadic and result from contaminated food (especially poultry) and exposure to environmental waters. Some C. jejuni infections (~1/1,000) lead to the development of Guillain-Barré Syndrome, the leading cause of acute paralysis in the world, as well as reactive arthritis and other sequelae. Despite the high prevalence of Campylobacter disease and some 40 years of research, the mechanisms by which C. jejuni causes disease remain incompletely understood and severely understudied. Phosphorylation of aspartate residues of bacterial regulatory proteins is a well-known mechanism for mediating changes in gene expression. However, it is increasingly recognized that phosphorylation of proteins at serine/threonine (S/T) residues also modifies protein function. The S/T phosphorylation system uses specific kinases to phosphorylate proteins, and phosphatases to remove the phosphates from S/T residues, in response to environmental signals. Importantly, this occurs in bacterial pathogens, modifying many virulence-associated characteristics. For the first time, our preliminary studies indicate provide new evidence that C. jejuni S/T phosphorylates eight proteins related to the critical pathogenic determinants of motility/chemotaxis, suggesting that S/T phosphorylation modulates C. jejuni virulence. We will define the S/T phosphorylation system in C. jejuni, according to the following hypothesis: Overall Hypothesis: C. jejuni phosphorylates proteins at S/T residues to modulate motility/chemotaxis and related pathogenesis characteristics, by means of novel S/T kinases/phosphatases. We propose a detailed study of protein S/T phosphorylation in C. jejuni, focusing on the mechanism by which the phosphorylation of motility/chemotaxis-related proteins affects their functions, as well as determining the proteins that affect the levels of S/T phosphorylation. We will use a combination of genetic, biochemical, and advanced phosphoproteomics approaches to achieve the goals outlined in these two specific aims: Aim 1. Determine the role of S/T phosphorylation for the function of motility/chemotaxis-related proteins, and Aim 2. Determine the roles of putative S/T kinase/phosphatase proteins in modifying C. jejuni proteins. Together, these will lay the groundwork for our long-term goal of identifying druggable targets to interrupt C. jejuni S/T phosphorylation and interrupting inter-host transmission and pathogenesis in humans.

NARRATIVE Campylobacter jejuni is the leading bacterial cause of gastroenteritis in the US and throughout the world, causing 140 million cases of acute diarrhea annually, >30,000 deaths in children <5 years of age; C. jejuni is also the leading cause of the acute paralytic disease Guillain-Barré Syndrome. This work will determine the mechanism by which the phosphorylation of C. jejuni proteins at serine/threonine residues modulates the virulence-related characteristics of flagellar motility / chemotaxis, biofilm formation, and central metabolism. The long-term goals of this project are to identify novel intervention points at which this signaling network may be interrupted, preventing both transmission between avian and human hosts, and pathogenesis in humans.